The present invention relates to diagnostic medical equipment and in particular to a bone densitometer providing an output indicating absolute risk of bone fracture.
Bone densitometers provide a measurement of bone mineral density (BMD) typically using x-ray or ultrasound measurement. Normally this BMD value is an areal density measurement, e.g., g/cm2, however, volume density measurements, e.g. g/cm3, may also be provided using, for example, tomographic reconstruction.
BMD measurements may be made at various locations on the body but are most frequently conducted on the bones of the lumbar vertebra, the femoral neck, or the os calcis of the heel.
X-ray and ultrasound densitometers are described in U.S. Pat. Nos. 6,438,201, 6,364,837, 6,277,076, 6,246,747, 6,215,846, 6,160,866, 6,081,582, 6,038,281, 6,027,449, RE361 62, 5,841,833, 5,840,029, and 5,748,704, among others, assigned to the assignee of the present invention and hereby incorporated by reference.
A raw BMD value has limited meaning to a physician or patient and so current densitometers normally provide a comparison of the measured BMD value to an established reference. One such reference is a T-score, which compares the patient""s BMD value to the expected value of BMD for a young adult of the same gender. The T-score provides a qualitative indication of risk of fracture in that the greater the negative value of the T-score, the greater the risk of fracture.
Alternatively, a logistic regression analysis may be used to determine a quantitative relationship between BMD and relative fracture risk based on a recognized mathematical relationship between decline in BMD and increased risk of fracture. This relationship has been determined prospectively in empirical studies of elderly populations and considers the difference between the patient and someone of the same age and gender.
Desirably, bone densitometry equipment would provide an indication of the patient""s absolute fracture risk. In this respect, T-scores and relative risk measurements are inadequate. For example, a 70 year old patient with a T-score of xe2x88x922 and relative risk of 4 has much greater absolute fracture risk than a 50 year old patient with the same T-score and relative risk.
The present inventors have recognized that measurement of BMD produced by densitometry equipment, cannot alone provide an indication of absolute fracture risk. To the contrary, current studies show that absolute fracture risk is strongly dependent on factors that are independent of BMD, in particular, age and gender. Other factors which affect absolute fracture risk include: whether the patient is a smoker, the amount of exercise the patient gets, how much the patient is on his/her feet, the patient""s history of fractures, the patient""s family history of fractures, and the long axis length of the patient""s hip (hip axis length). It is likely that additional risk factors will be discovered.
The present invention therefore provides a bone densitometer that accepts additional patient data to produce an output measurement of absolute fracture risk. The physician and patient are presented with this absolute fracture risk contemporaneously with the measurement of BMD, reducing patient confusion about T-scores and relative risk, and eliminating the need for cumbersome additional calculations by the physician.